Figure 9

Lhx9 mediates a caudal to rostral change in the turning of dI2 axons. Lhx9 and GFP were expressed ectopically in dI2 and V1 neurons, utilizing the Cre/lox system and the EdI2/V1 enhancer (EdI2/V1::Cre + pCAGG-LoxP-STOP-LoxP-Lhx9-IRES-GFP). (A) At the caudal sacral level the commissural dI2^Lhx9 axons turn caudally (A, A1). At the rostral sacral level axons turn rostrally and caudally, forming a crisscross pattern (A, A2). Rostral to the lumbar level dI2^Lhx9 axons turn rostrally (A, A3, A4). A longitudinal fascicle at the ventral funiculus (VF) is present at the ipsi- and contra-lateral sides of the floor plate (A, A4). (B) Schematic representation of the caudal/rostral axonal projection of three control neural tubes (dI2^GFP) and of six manipulated neural tubes (dI2^Lhx9). The vertical lines represent the location of the limbs. (C) Schematic illustration of the phenotype of dI2^Lhx9 axonal cues. c, cervical level; b, brachial level; FP, floor plate; l, lumbar level, s, sacral level; t, thoracic level. The asterisks represent the level of the limbs. The white arrows point to the rostrally projecting axons. The magenta arrows point to the caudally projecting axons. The crossed arrows point to the crisscross axonal pattern. Scale bars: 200 μm (A); 150 μm (A1, A3–A5); 100 μm (A2).